The present invention relates to a semiconductor device, a write strategy generating method, and a write strategy generating program, and particularly to a technology effective when applied to a semiconductor device mounted in an optical disk apparatus and for controlling writing of data in an optical disk.
In a writable or rewritable optical disk such as DVD-R (DVD-Recordable), DVD-RW (DVD-Re-Writable) or the like, laser light is applied onto a recording surface of the disk, so that a thermal change occurs in an optical storage medium to record information therein. As a method of controlling laser light for recording information in the optical disk, there is known, for example, a method of modulating laser light by a recording pulse having a time width corresponding to information to be recorded, thereby forming a recording mark having a length corresponding to the information to be recorded, on its corresponding optical disk.
On the other hand, there is also known a method of controlling laser power for forming a recording mark by a pulse train including a plurality of short pulses (multipulses) and not forming just one recording mark for recording information in the optical disk by one laser pulse as in the above method. This method is referred to as “write strategy”. According to this method, thermal accumulation on a recording surface of the optical disk is reduced as compared with a method of applying a single recording pulse. Therefore, a temperature distribution on a recording surface with a recording mark formed thereon can be made uniform, so that the recording mark is prevented from being brought into a tear-shaped form. It is thus possible to form a recording mark having a preferred shape. In the multipulse-based write strategy, however, no problem arises at recording at a normal speed, but the amplitude of a pulse changes due to overshoot and undershoot at high-speed recording, thus causing a fear that the amount of heat of the optical disk may not be controlled accurately, and a recording mark having a suitable shape may not be formed.
As a method of solving this problem, there is known a write strategy of a system using a recording pulse including a top pulse for preheating the recording surface of the optical disk, an intermediate bias part at which a time width changes according to the length of a mark to be recorded, and a last pulse for adjusting the shape of a read end portion of the recording mark (e.g., Patent Document 1).
As a write strategy of another system, there is also known a write strategy in which the positions of a top pulse and a last pulse and their pulse widths are changed according to space lengths lying immediately before and after a mark to be recorded, in consideration of thermal interference at recording and optical interference at reproduction due to changes in space length before and after the recording mark. In addition to the above, there is also known a castle-type write strategy using a recording pulse configured as a unique shape including a top pulse, an intermediate bias part and a last pulse.
As described above, the optical disk apparatus generates a recording pulse of the optimum recording power at at least one predetermined write strategy and controls laser light by the recording pulse to thereby record information in the optical disk. Variations however occur in the optimum recording pulse timing position of the recording pulse and the like due to variations in performance of the optical disk apparatus itself, variations in optical disk, etc. When a recording pulse timing position and the like of a write strategy relative to the mounted optical disk are not appropriate, a mark length of a recording mark recorded in the optical disk and its edge position become inappropriate, so that the quality of reproduction such as jitter characteristics, an error rate or the like is degraded. As a related art for optimization of a write strategy, which is used for solving such a problem, there are known those disclosed in, for example, Patent Documents 2, 3, 4 and 5.